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stevenKm (Mechanical) (OP)
3 Apr 12 16:59
Hello everyone. First, a disclaimer: I am not a certified mechanical engineer nor HVAC technician.  However I am a mechanically inclined facilities manager. I've been reading through the forums and this seems like a friendly group with a wealth of knowledge.

Here's the problem:  I've got a chilled water valve that is not closing and I've been having to control temps by manually shutting or sometimes just cracking open the shut off valve on the cold water supply line.  I have had multiple certified HVAC technicians come out to trouble shoot the problem but none of them can seem to fix it.  I've been told that the valve is functioning properly and that it "MAY" be a control issue.  The most recent service call seemed to temporarily fix the problem. The technician said he reset the controller. However, now the problem has reappeared and the cold water valve isn't closing again.

The system is less than 5 years old.  I was also told that my predecessor had to have the valve or actuator replaced in the past.  

I don't know how much faith I put in the local technicians to solve this and I'm looking for ways to at least make sure that they are correctly identifying the issues.

I have attached photos of the chilled water actuator and valve.

Here are my questions:
1. What is the best way to test the proper functioning of both the valve and the actuator?

2. If it is indeed a control issue, how likely is it that "resetting" the controller would have worked temporarily?

3. If this is indeed the second broken valve or actuator in less than 5 years, what might be causing this premature failure?

Any help or advice is greatly appreciated.  Thank you!
MintJulep (Mechanical)
3 Apr 12 21:50
The valve command is the control output.

What are the control inputs?

What is the control supposed to do with the output in response to the inputs?

 
SAK9 (Mechanical)
3 Apr 12 22:37
Disconnect the actuator and   manually operate the valve to mark on the valve stem fully open and fully closed positions.Reconnect the actuator and operate the actuator to mark on the stem positions correponding to actuator at 0% and actuator at 100%.If they are different you have a problem.
KiwiMace (Mechanical)
4 Apr 12 3:28
What pressure is the valve trying to close against?  or, How tall is your building?  Valve/actuator may not be designed for the operational conditions.

The best way to test it is to take it out of the line and stroke it from the DDC signal, watching the valve open and close in proportion to the signal.  You can do this in the line, but you will never be sure that the valve (butterfly or globe) is still connected to the valve stem.  This kind of failure can give intermittent results.

 
stevenKm (Mechanical) (OP)
4 Apr 12 14:23
Thank you everyone for the replies.  I tried all of your suggestions with the valve still in place.  Finding a time when I can take the valve out of the the line will be hard.  The building is hardly ever empty.

I have disconnected the actuator and manually opened and closed the valve.  The stem is travelling roughly 15mm (5/8") when operated manually and when it is getting DDC.  Is this the proper travel distance for such an actuator?

The pressure in the chilled water supply line fluctuates between 40psi when the valve is closed and 30psi when the valve is open.  The total building height is 24' at its max and the HVAC is located on the first floor.  I was told by the local technicians that as long as the pressure was under 80-90psi that the valve should be able to operate properly.

Because I can watch the line pressure change with the operation of the valve, my thought is that the stem is still connected to the valve.

Again, thank your for your input and if you have any other suggestions on what to check next, please let me know.
SAK9 (Mechanical)
4 Apr 12 18:25
It appears the valve is functioning as designed.The next step would be to look at the seats for any erosion for which you need to take it off line and do a pressure test.Five years is rather early for a seat erosion failure but possible if it had been operating close to shut off most of the time.
rogzog (Mechanical)
8 Apr 12 19:45
In your picture I see two valves. The main valve and possibly a bypass valve. You may need to check both valves for full closing with their actuators.
 
Helpful Member!  pretendfarmer (Mechanical)
11 Apr 12 23:18
Hi stevenKm,
(1)From your picture it appears that you may have a 1/3-2/3 control valve arrangement so that the small valve is modulating open until it cannot satisfy the load and then the larger valve starts to open. When the larger valve starts to open, the smaller valve may modulate shut (or may not, depending on how the valves were selected and what the control scheme is). Trane is printed on the actuators so you can contact your Trane rep and ask him (or her) what the close off differential pressure rating is for the valve/actuator assembly. Some actuators cannot close off against very high pressure differentials. When they can't close off, they bleed through.
(2)The valves may be doing exactly what the control scheme is telling them to do. You need to find out what the control sequence is for that air handler.
(3)Are the pumps variable speed or constant speed? If constant, they may have the valves programmed to never go completely closed so as to not dead head the pump.
There are many possibilities....

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